A new model structure for the hydrolysis step is introduced in the IWA anaerobic digestion model no 1 (ADM1) in order to better represent the bioaccessibility of particulate organic matter. Two particulate organic matter fractions for waste activated sludge (WAS) samples were defined: a readily hydrolysable fraction (Xcr) and a slowly hydrolysable fraction (Xcs). These fractions were hydrolyzed according to a surface-limiting reaction. Batch anaerobic digestion test of untreated WAS was used to develop the model and calibrate the kinetic parameters and biomass concentrations. The validation was carried out with a similar substrate than the calibration but a thermal pretreatment was applied at two different conditions (110°C and 220°C). The behavior of thermophilic anaerobic digestion of WAS samples was effectively represented by the proposed model. No changes among kinetic parameter sets were done and the model is able to represent produced methane volume following the intrinsic changes of the WAS composition through the different thermal pretreatment conditions. Moreover, estimated parameters in 20days of batch anaerobic digestion test were representative of continuous anaerobic digestion in a full-scale digester.

The viability of the anaerobic membrane bioreactor (AnMBR) technology for the treatment of sewage sludge has been studied under mesophilic and thermophilic conditions. Coupling membrane filtration with the digestion process allows the digestion to be operated with longer solids retention time (SRT), and the volumetric load can be increased considerably compared to the conventional completely stirred reactor process. Maximum SRT is conditioned by the total solids concentration and the viscosity of the digested sludge. Values of 50 and 30 days for 55 and 35°C were obtained in the experimental platforms. Organic loads of 6.4 and 4.6gCOD/(L·d) were successfully treated at 55 and 35°C, respectively, representing a significant digester volume reduction compared to conventional systems. The performance of thermophilic and mesophilic AnMBRs were compared, and the same sludge biodegradability was measured. The difference was the distribution of the inert COD among the soluble and particulate fractions. Better filtration performance was observed in the thermophilic system, where a larger flow could be attained and the lower viscosity enabled operation with higher SRT. However, increased irreversible fouling at higher temperature was shown to require optimised chemical cleaning strategies to extend membrane lifetime. In conclusion, AnMBR offers an extensive opportunity for the treatment of waste streams with high-solids content waste streams, where membrane filtration is one of the most promising technologies for decoupling solids and hydraulic retention times.

This paper presents a study concerning the optimization of a Waste Water Treatment process. The process deals with carbon and nitrogen removal and includes activated sludge reactors coupled with an anaerobic digestion reactor. Nitrification and de-nitrification biochemical reactions are due to the biological activity of heterotrophic and autotrophic micro-organisms occurring inside the reactors. Rigorous Plant-Wide models that represent the main biochemical transformations have been constructed as per the CEIT approach [1]. The energy consumption for each Physical Unit Operation (P.U.O.) involved in the flow-sheet is evaluated and a full link is made between the biological activity and the electrical demand or production. Steady-state mathematical optimizations are then computed and the influence of primary settling efficiency on electrical autonomy is quantified and demonstrated. The ammonium recycling from digestion to activated sludge reactors is also demonstrated to be a limiting factor for the overall energy efficiency, as well as the C-substrate availability for denitrifying. Some conclusions are then drawn to improve the global electrical efficiency of the system.

The selective removal of ammonia from industrial waste streams and the conversion of the organic matter to biodegradable compounds, without excessive mineralization of the carbon has been investigated over powder and pelletized titania- and zirconia-supported Pt catalysts in the wet air oxidation (WAO) of aqueous solutions at 200 degrees C under 36 bar of air, in batch and trickle-bed reactors.Ammonium acetate was chosen as a model compound (58 mmol L-1, Total Organic Carbon, TOC = 1392 mg L-1, Total Nitrogen, TN = 812 mg L-1). In the absence of any catalyst, very little ammonium was removed. With addition of a Pt catalyst supported, NH4+ was completely eliminated from the reaction mixture and converted to dinitrogen with a selectivity higher than 97.5%. The treated effluent contained very low concentration of nitrates as a by-product. Interestingly, the platinum catalysts were very little active in the mineralization of the organic carbon, so that the effluent could be post-treated in a conventional biological plant. The catalysts showed the same performances over recycling experiments in a batch reactor. Moreover, the pelletized catalysts were shown to be stable upon preliminary continuous experiments in a trickle-bed reactor over a period of 350 h. The 3%Pt/TiO2 catalysts were significantly more active than the 3%Pt/ZrO2 catalysts in batch and continuous experiments. (C) 2012 Elsevier B.V. All rights reserved.

Coupling the activated sludge and the ozonation processes is an efficient, although expensive, solution for sludge reduction. A better knowledge of the mechanisms involved in the degradation of various sludge fractions by ozone is needed to optimize the coupled process. The objectives of this study were to determine the biodegradability of ozone-solubilized endogenous residue, the action of ozone on the active biomass and the solubilization yield of these two main sludge fractions. Batch tests were conducted with slug input of ozone stock solution into fresh or aerobically digested synthetic sludge. Biodegradability of the solubilized endogenous residue was increased by ozonation by up to 0.27 g BOD5/g CODi. Ozone caused biomass lysis, as opposed to an increase in maintenance needs, as shown by a correlation between the decrease in microbial activity and viability. Lysis caused by ozonation was associated with a solubilization of 20% of the lyzed cell COD mass. Solubilization yields were of 9.6 and of 1.9 to 3.6 g COD/g O3 for fresh and aerobically digested sludge, respectively. Design of sludge ozonation processes should account for the variability between the solubilization yield and biodegradability of the various sludge fractions.

Cette publication a pour objectifs de decrire la procedure utilisee pour realiser la reconstitution d’une eau usee artificielle et de presenter les resultats des essais en laboratoire puis, sur une plate-forme de tests, les resultats d’utilisation de cette eau usee reconstituee artificiellement. Les eaux usees artificielles doivent etre aisement reproductibles quels que soient les sites sur lesquels elles seront utilisees; les melanges de matieres premieres doivent etre aussi limites que possible; dans ces travaux, la composition d’eau usee ciblee est une composition relativement classique d’eaux usees domestiques, soit : matieres en suspension (MES) 350 mg/L; demande biochimique en O 2 mesuree a 5 jours (DBO 5 ) 400 mgO 2 /L; demande chimique en O 2 (DCO) 880 mgO 2 /L; azote total Kjeldahl (N-NTK) 80 mgN/L et le phosphore total (P) 10 mgP/L; la biodegradabilite de l’effluent reconstitue ne doit pas etre trop rapide, c’est-a-dire comparable avec le fractionnement d’une eau usee urbaine classique. Globalement, cette etude donne des resultats tres satisfaisants. Nous avons pu montrer la reproductibilite de l’effluent reconstitue, ainsi que la fiabilite de la reconstitution des lors que les conditions optimales de mise en oeuvre sont maitrisees. Par ailleurs, les resultats de sortie des filieres restent tres proches de ceux obtenus avec l’eau usee urbaine qui les a alimentes pendant 3 annees.

Enhancing waste activated sludge (WAS) anaerobic digestion by thermal pretreatment has become of high interest. However, thermal treatment has been mainly combined to mesophilic anaerobic digestion. This paper presents the combination of sludge thermal pretreatment (110, 165 and 220°C) and batch thermophilic anaerobic digestion (55°C). Optimal conditions of thermal pretreatment were shown to be 165°C, involving a chemical oxygen demand (COD) and volatile solids (VS) solubilisation of 18 and 15% and a biodegradability increase from 47 to 61%. Treatments at 165°C were carried out in electric and steam modes and no significant difference on the impact of heating mode on sludge anaerobic biodegradability was observed. Moreover, it may be recommended not to carry out successive batch experiments to assess thermophilic BMP of sludge as accumulation of volatile fatty acids (VFA), particularly propionate, and a decrease of VFA uptake rates may occur. However, thermal pretreatment at 165°C allowed the decrease of propionate accumulation and an higher methane production.

Pour repondre au probleme de l'augmentation de la production de boues dans les stations d'epuration municipales et industrielles, due notamment au durcissement des normes et a l'augmentation du taux de raccordement aux reseaux d'assainissement, ONDEO-Degremont a developpe une nouvelle technologie de reduction de la production de boues agissant directement au coeur de la filiere de traitement de l'eau : BIOLYSIS®. S'appuyant sur l'experience de deux prototypes a l'echelle industrielle, ce travail presente des resultats concernant les effets des deux procedes BIOLYSIS® O et BIOLYSIS® E sur la production de boue, les performances d'epuration et la qualite des boues residuelles. Une analyse economique des procedes est egalement proposee.

Management of the excess sludge production resulting from biological wastewater treatment is one of the most important economic and environmental issues for the next decade. New stringent regulations regarding sludge treatment and disposal imposed in several countries as well as social and environmental concerns, have resulted in an increasing interest in processes allowing the reduction of excess sludge production. Following a 5 years research program, Ondeo-Degremont has developed two processes, Biolysis(R) O and Biolysis(R) E, designed to reduce sludge production during biological wastewater treatment. Experiment performed with Biolysis(R) technologies confirmed that high (up to 80%) reduction of excess sludge production can be reached while good treatment performances are maintened, in agreement with regulation standards. Economical data demonstrate the competitiveness of Biolysis(R) processes. Such processes appear to be a valuable alternative to solve the problem of sludge treatment, to protect operators from the evolution of legislation of sludge treatment and from risks inherent to final sludge disposal.

The use of ozone to attack soluble or solid recalcitrant compounds is often necessary to comply with environmental standards. In order to optimize ozone dosage its action must be properly targeted. Competition for ozone between soluble compounds and solid particles was studied using off-gas ozone concentration profiles. Deduced gas absorption enhancement for each matter type, alone and mixed, indicated non-classical competition. Results can be explained by the mass transfer film concept in the presence of reactive particles. Besides classical influential parameters (concentration and reactivity towards ozone), the temporary size distribution of solid particles related to the thickness of the effective liquid film must be considered.

Ozonation is a favourable technology for organic and mineral excess sludge production (ESP) reduction. This study confirms that in a continuous process, 100% organic ESP reduction can be achieved. Such efficiency is mainly the result of the solubilizing action of ozone, as 80% of organic ESP reduction observed can be explained by this phenomenon. Continuous and batch experiments show that this 80% of ESP reduction is accounted for by one part which is biodegraded (50%) and the other part which is not biodegraded (30%). The letter explains the increased outlet COD. Moreover mineral sludge accumulation in the reactor can be reduced using ozone. In fact, mineral matter is also solubilised by ozone treatment, but to a lesser extent. Consequently, to totally prevent mineral matter accumulation, particulate matter must be removed. Considering nutrient removal, nitrification potential remains constant, even for no ESP conditions. But to deal with P removal, an ESP reduction process including a combined physical-chemical precipitation of phosphorus in the combined system is necessary.

Procede de reduction de la production de boues des stations d'epuration des eaux usees urbaines ou industrielles, par voie anaerobie, caracterise en ce qu'il est independant de la ligne de traitement des eaux et en ce qu'il comporte au moins une etape aerobie de solubilisation biologique par voie enzymatique thermophile, associee a une etape de digestion anaerobie mesophile, thermophile ou associant ces deux modes de fonctionnement.

The release performances of an organic and mineral activated sludge matrix were studied for a wide range of disintegration treatments like mechanical, thermal, thermal-chemical and oxidative disintegration techniques. The maximal COD release was 35% of total COD after 24 hours contact time at 95 degrees C. A limiting value of 60% COD release was obtained for 500 and 700 bars after 10 passes. Concerning theoxidative disintegration techniques (O3 and H2O2), a limiting value of around 60-65% of TOC release was observed. Therefore, it was hypothesised that thermal and mechanical treatments allow mainly for breaking apart the micro-organisms while the oxidative treatment destroys the sludge flocs and disrupts the micro-organisms. A release effect of the mineral fraction is observed only oxidative disintegration techniques.

A combined system associating activated sludge and ozonation was evaluated for the treatment of urban wastewater. Experiments have shown that 70% reduction in sludge production can be reached (compared to a reference system running in low loaded conditions Y(obs) = 0.28 g VSS.g COD(-1)) by applying an ozone dosage of 0.05 g O3/g VSS(treated) Recycling of the ozonated sludge to the aeration tank induces a slight increase in effluent COD, but the biological treatment performance is maintained. Nitrification capabilities are not altered by the sludge reduction process and active biomass measurements revealed that autotrophic biomass seems to be less affected than the heterotrophs. Significant improvements in sludge settling characteristics are observed.

L'elimination des boues produites lors de l'epuration biologique des eaux usees fait partie des enjeux majeurs de la prochaine decennie. Les contraintes qui pesent sur les filieres classiques orientent les recherches vers des procedes de reduction de la production de boue au sein de la filiere de traitement de l'eau. Ainsi, l'association entre une etape d'oxydation chimique par l'ozone et un traitement biologique par boues activees peut conduire a une reduction significative de la quantite de boue produite. Basee sur une double approche, experimentale et de modelisation, l'analyse des mecanismes de la production de boue montre l'influence capitale des processus d'accumulation des matieres organiques inertes particulaires provenant de l'effluent a traiter et issues du processus de deces. Si l'etape d'ozonation permet de rendre biodegradables ces fractions inertes, les simulations montrent qu'il est possible d'atteintre une reduction totale de la production de boue. Les essais discontinus d'ozonation de boue mettent en evidence une acion solubilisante de l'ozone sur la matiere particulaire, une augmentation de la biodegradabilite et une inactivation significative des microorganismes. Les resultats obtenus permettent de construire un modele d'action de l'ozone sur la boue qui, couple au modele du procede biologique, permet de confirmer par la simulation l'interet du procede combine. Le couplage entre l'etape d'ozonation et le procede biologique permet de supprimer la production de boue organique excedentaire et conduit a une reduction de la production de boue minerale. L'optimisation du mode d'apport de l'ozone apparait determinante pour garantir l'efficacite de l'etape d'ozonation. Ce travail met en evidence l'apparition d'un talon de DCO refractaire dans l'effluent, l'amelioration des caracteristiques de decantation et le maintien des activites nitrifiantes. Il montre l'applicabilite de ce procede et precises les conditions dans lesquelles il peut etre mis en œuvre

New strategies for sludge stabilization and mineralization need to be developed since the use of sludge in agriculture is debatable and sludge incineration cannot be a systematic solution. Minimization of sludge production should be preferred. In this work, the effect of ozone on activated sludge solubilization and mineralization during batch experiments is assessed by establishing carbon and ozone mass balances. After extended ozonation of the sludge, more than 90% of the particulate carbon is modified. Depending on the experimental conditions, from 15 to 50% is found in a soluble form and from 35% to 95% was mineralized. The VSS / SS ratio decreases from 86% to less than 50% illustrating the sludge mineralization. The initial rate of ozone consumption by the sludge is very high (estimated value: 30 mgO(3) / g VSS.min) and corresponds to high rates of carbon solubilization and mineralization. More than 50% of the carbon obtained after ozonation is found to be readily biodegradable using a short-term BOD procedure.